Study and Analysis of Travelling Wire Electrochemical ... · Numerical model develop is created in...

© 2018 JETIR June 2018, Volume 5, Issue 6 www.jetir.org (ISSN-2349-5162)

JETIR1806703 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 18

Study and Analysis of Travelling Wire

Electrochemical Spark Machining

Sukhjinder Singh Sandhua and Ramandeep Singhb, a Assistant Professor, Department of Mechanical Engg, S. B. S. S. T. C., Ferozepur, 152004, INDIA b Assistant Professor, Department of Mechanical Engg, S. B. S. S. T. C., Ferozepur, 152004, INDIA

Abstract

Travelling Wire-ECSM can be used for machining insulating material on large scale. OFAT (one-

factor-at-a-time) technique is used to perform experiments on TW-ECSM setup. Effective

combination of maximum MRR and better surface finish is subject of concern. If MRR is high than

surface finish will be low, so by optimization of parameters we can get optimum MRR and good

surface finish. There are several parameters like applied voltage, electrolyte concentration, electrode

distance, and feed rate etc. on which MRR and surface finish depends.

Key words: ECM; EDM; ECDM; TW-ECDM; TW-ECSM

Introduction

Travelling Wire: Electro-chemical Discharge Machining (TW-ECDM) is a modern non conventional

machining method. It is a combination of Electro-chemical Machining (ECM) and Electro-discharge

Machining (EDM). Travelling Wire- Electrochemical Discharge Machining (TW-ECDM) is also

known as Traveling Wire: Electro-chemical Spark Machining (TW-ECSM) process. It is extension

of Electro-chemical Discharge Machining (ECDM) process. It can machine hard materials like

ceramics, composites, alumina, glass etc. so it is important. The basic principle of TW-ECDM has

similarity with ECDM process. TW-ECDM mainly uses a continuous travelling wire electrode to

machine the component. In TW-ECDM method, high density bubbles formation due to electrolysis

and then breakdown of gas film due to their coalescence causes the spark in TW-ECDM. Micro

bubbles start forming as the supply voltage exceeds the critical value. There exists a dielectric film

between the tool surface and electrolyte. This dielectric film is formed due to bubble coalesce.

Occurrence of electrical discharge between tool and working component are caused by high

electrical field in the gas film region. After this action, rest of the process is same as Electro

chemical Machining. Due to this electrochemical reaction there is formation of the positively

charged ions and gas bubbles. Space between the tool and working component contains the gas

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bubbles formed in the process. There is an electrical discharge action between the tool wire and the

electrolyte in the gas bubble regions. As the supply voltage increases the breakdown voltage level of

gas bubbles spark initiation takes place. Amount of supply voltage controls the spark discharge level.

As the voltage increases, the intensity and energy of spark formed also increases. Insulating

component is placed near to the spark. Material removal of the component takes place due to 3

processes. These processes are melting, vaporization and energy transmission. MRR depends mainly

on parameters like supply voltage, electrolytic concentration, tool wire feed rate, pulse time.

1.1 Basic Principle of Travelling Wire-ECDM

In TW-ECDM process combination of 2 processes EDM and ECM are merged together. In this

process Electrode is inside the electrolytic solution. This electrode acts as anode. Machining of

materials like composites, ceramics, and glass can be easily done using this process. Electrode in this

process is a movable wire which is continuously travelling during the process. In TW-ECDM

method, high density bubbles formation due to electrolysis and then breakdown of gas film due to

their coalescence causes the spark in TW-ECDM. As the supply voltage increases the breakdown

voltage level of gas bubbles spark initiation takes place. There forms a gas bubble layer between the

electrolytes surrounding the cathodic component. These formations of film between the 2 causes

spark discharge between the anode tool and cathode work piece. Due to electrical discharge spark

generates. As the spark generated high heat is produced. This high heat causes the material removal

from the working component. It is basically a non traditional approach of removing material. It is

mainly used for the purpose of slotting and slicing in components. As the heat generated due to the

spark is high, wire has to move in order to prevent it from breakage. Wire is kept at high tension

during the process. There is a optimum speed at which wire to be move, This speed should not be

too slow or neither be too fast. Too slow speed will cause wire breakage due to excessive heat. Spark

will form only once the supply voltage exceeds the critical voltage. The main feature of this process

is it avoids the limitation of working at depth compared to ECM. Also this method can be applicable

for the micro machining.

Fig.1.1 Basic elements of the TW-ECDM process




1.2 Requirement of TW-ECDM Process

ECDM process is a hybrid machining process and it is a combination of ECM and EDM process. It

has application in machining of hard material which is difficult to machine by ordinary machining.

ECDM is used to machine non conducting material, complex shapes, to produce holes in electrically

non-conductive material. It can also machine advanced non conductive materials. TW-ECDM was

introduced to machine those which were hard to machine by using ECDM process without

machining large materials i.e. grooves, complex shapes and generating complex shapes on the

working insulating component. TW-ECDM can produce intrinsic shapes. Also amount of material

removed in producing this shapes are very less. Common problems in operating this process is wire

movement and care of wire guides during the wire movement. ECDM process has some problems

like limiting the depth during machining. New developments are taking place in ECDM process day

by day varies rapidly. etc. ECDM process is used to produce holes in electrically non-conductive material.

The process is difficult to install and generally required high maintenance effort. Still these problems

are less compared with other processes along with the luxury of machining hard materials. TW-

ECDM is a micro machining process so we desire good surface finish and this process gives good

surface finish. By proper controlling of various process parameters, good accuracy, better surface

finish, better machining rate can be achieved with minimum material wastage. Machining of

materials like composites, ceramics, and glass can be easily done using this process. The main

feature of this process is it avoids the limitation of working at depth compared to ECM.

1.3 Application of Travelling Wire-ECDM

The Travelling Wire Electro-chemical Discharge Machining (TW-ECDM) method is used mainly

for working on insulating materials like glass, hard ceramics & new composites. The TW-ECDM

process also founds it application for micro-slotting operations on hard materials like ceramic.

TW-ECDM process can slice the non-conductive materials like glass, ceramic.

TW-ECDM process can use for shaping electrically insulating component like glass,

ceramics.

1.4 Benefits of TW-ECDM

TW-ECDM process can machine electrically insulating materials.

TW-ECDM process can easily slice the material.

TW-ECDM process can make desired profile on hard materials.




Machining cost is low as compared to other processes.

1.5 Limitations of TW-ECDM

TW-ECDM process can machine only non-conducting materials. So Machining is limited.

In TW-ECDM process, Due to side sparking over cut occurs.

In TW-ECDM process, Surface finish is very poor.

In TW-ECDM process, material removal rate is poor.

2. Literature Review

Sir Joseph Priestly did experiments on metal and found the principal of erosion and that erosion

was taking place because of sparking but he did not do it for machining. However, later Lazarenko

carried out metal machining using spark erosion technique. British scientist first patented the electro

spark machine. Later, Lazarenko provided prelude the manufacturing process by introducing ECDM

process which was actually sparked erosion machining. In later seventies, the research work was also

done for generating complicated machining surface on very hard conducting materials. In 1968, a

method which used electrical discharge system for drilling a hole in glass was explained by Late

Professor H. Kurafugi. As the time passed use of ECDM increased and various researches was

carried out to increase to effectiveness of this process and to explore new areas in which this process

can be used. Following are some research works which have already been done by researchers in

field of ECDM and TW-ECDM. Peng and Liao [1] found out that in TW-ECDM, a voltage higher

than the transition voltage was required for the clear start discharge around the wire. The relationship

between current and voltage can be emphatically indigent when applied voltage is just bigger than

the move voltage. For the machining of high-quality non-conductive materials, the ECDM process

has been proved as a potential procedure. For cutting the little size (10–30mm measurement) optical

glass and quartz bars, travelling wire electrochemical discharge machining (TW-ECDM), a recently

created innovation, was utilized. Research was done on electrical–thermal scratching impact and its

plausibility. The pulsed dc power showed some advantage like better start security and more start

vitality discharge extent over consistent dc power. For machining glass and quartz materials the

input power was adjusted to obtain the appropriate frequencies and obligation variables. It was found

that the predominant elements of bubbles reaction were particle interpretation rate, electrolyte

inundating profundity and the convergence of the salt. Liu et al. [2] reported that material removal

rate was diminished by a high connected voltage or long pulse duration. They have showed that a




low material removal rate (MRR) was obtained by using the routine WEDM-LS method could mean

(MRR), and more important, a high danger of wire breakage was experienced in wire cutting.

Tandon et al. [3] investigated another method that utilized electrochemical spark machining

(ECSM) for cutting and drilling hole in fiber reinforced composites (FRP). Kevlar fiber reinforced

epoxy and glass fiber reinforced epoxy was used as work materials and was used as work material. A

"one variable at a time" approach and configuration of examination idea were used for parametric

investigation of the procedure. MRR, TWR, OC was found to increase and relative device wear was

found to decrease with increase in connected voltage over the anodes. Bhattacharyya et al. [4]

suggested another innovation for the ECDM procedure. This ECDM method can easily machine

ceramics made up of silicon nitride material. He develops the advancement of a 2nd

order, non linear

numerical method to form a relationship among the operating parameters. These parameters are

supply voltage, focus of electrolyte & terminal hole. These relations are develop by keeping in mind

the machining criteria such as MRR, overcut in radial direction, width of heat affected region.

Numerical model develop is created in light of reaction surface approach (RSM) utilizing the

significant test information, which are gotten amid an ECDM smaller scale penetrating machining of

silicon nitride. Along with it he created fluctuation examination using ANNOVA & done a test to

confirm the fit & ampleness of numerical model. From the research work it has been concluded that

supply voltage directly controls the material removal rate, ROC and HAZ width. Yang, et al [5]

indicated the common consequences originated during the machining process of TW-ECDM. From

the work it was shown that materials having high strength, fragility, and electrical insulation can be

easily worked by using this process. Cathode component in the electrolyte is surrounded by the

hydrogen bubbles formed during the chemical reactions. Thin film layer starts forming on the

electrode. In this way cathode gets detached from the electrolytic solution. Condition when supply

voltage increases the basic voltage, persistent release happens. The material close to the electrode is

removed by the release disintegration and compound drawing. The utilization of TW-ECDM to cut

electrically protecting materials has just as of late been researched. Nonetheless, the breakdown of

the gas in the bubbles and the vibration of the wire in TW-ECDM unequivocally influence the shape

precision. Over cut quality during the process can be enhanced by adding silicon grating in the

electrolytic solution. Contemplation of process having abrasive cutting along with chemical etching

is used to consolidate the discharge. Doloi et al, [6] carried out the machining of hylum based fiber

composite using ECDM. This method can likewise utilize for miniaturized scale cutting & scoring

on non leading materials. Their main area of concern was to form a framework to analyze parametric

impacts of MRR.




Cao et al, [7] that Micro- ECDM was concentrated on so as to enhance the machining of 3D smaller

scale pieces of glass. Electrolytic concentration, feed rate, supply voltage, swirling velocity, pulse on

& off time duration in the process are varied in order to get a refined microstructure surfaces. In

order to form a steady gas film on the device surface on less voltage supply, another contact

indicator, taking into account a heap cell, was utilized; the drenching profundity of the instrument

terminal in the electrolyte was lessened however much as could reasonably be expected. Han, et al

[8] develop a new technique to increase the surface finish & flash discharge dispersion of wire using

Wire ECDM in which the wire surface is not smooth. In case of normal Wire ECDM problem is to

operate under low cutting speed along with low start and release event of the wire surface when it is

moving. Initial tests exhibited that by using tool wire having surface harshness of Ra= 0.14 μm

machining having 1.1 mm was unable to access because of the absence of spark dispersion on the

tool wire. They observed that wire surface roughening has improved flash release circulation over

the surface of apparatus and have brought down the working voltage. Side protection of the wire was

also observed with minimization of the responsive wire surface territory. Bhattacharyya, et al [9]

brought attention to the fact that for the machining of non-conductive ceramic materials,

electrochemical discharge machining (ECDM) has showed great potential as compared to other non-

conventional machining strategies. They examined the fundamental material evacuation instrument

in the ECDM process for the effective machining of non-leading ceramic materials with enhanced

machining rate and greater machining precision. The ECDM procedure is dependent on different

procedure parameters like the connected voltage, gap between electrode, the temperature,

concentration and kind of electrolyte; the shape, size and material of the terminals; the way of the

power supply. Experiments have been done in accordance to the impacts of the different procedure

parameters of ECDM. Mechatronics was the highlight of the created machining set-up used for

doing exploratory examinations. .For machining of aluminum oxide clay work pieces, trial

examinations have been conducted using ECDM and material removal rate and over-cut phenomena

have been observed under shifting procedure parametric conditions. For example, connected voltage

(70±90 V),and electrolyte focus (20±30%). NaOH arrangement with differing fixation was taken as

the electrolyte. For the boring operation of ceramic work-test, a pulse d.c. electric supply has been

used. Basak, et al [10] proposed a hypothetical model for the clarification of flash era amid

electrochemical discharge machining (ECDM) process. The procedure is normally termed

'electrochemical arc machining' (ECAM) at the point when the machined material is electrically

conducting. It is termed 'electrochemical discharge machining' (ECDM) for non-conducting work

materials. In both cases electrical discharge happened through the electrolyte and assumed as a basic

part, the system of spark area has not been researched effectively. Guo et al [11] observed the




discharge mechanism in electrochemical discharge machining (ECDM) of a particulate reinforced

metal matrix composite. They also developed a model to uncover the electric field that build up on a

hydrogen bubble in ECDM procedure. Experiments were conducted to verify the model and the test

results matched well with the anticipated values. The trial results showed that for advancement of

arcing activity in ECDM, an increment in current, duty cycle, pulse span or electrolyte concentration

is required. Adhikary et al [12] used electrochemical flash machining (ECSM) procedure for

effective cutting of quartz utilizing a controlled feed and a wedge edged tool. Both cathode and

anode were utilized as a tool despite of regular belief that only cathode acts as a tool. To machine

quartz plates, they have utilized ECSM with reverse polarity (ECSMWRP) and also ECSM with

direct polarity (ECSWDP). Due to chemical reaction, generation of profound pit on the anode (as a

tool) and work piece interface was observed in ECSMWRP. The possibility of dissolution of quartz

into solution because of chemical reaction was also validated by the chemical analysis of electrolyte

solution after the ECSM experiments. Reverse polarity showed advantage of faster cutting rate of

quartz plate as compared to direct polarity. But higher overcut, tool wear and surface roughness was

observed in reverse polarity as compared to the direct polarity machining. Difference in the mode of

material removal in ECSMWDP and ECSMWRP was shown by magnified view of the machined

surface. The cutting was also possible by smaller auxiliary electrode. Fascio et al[13] worked on

MEMS. They proposed micro fabrication of glass because glass has its unique properties like

transparency, non chemical reactive, non conductive to heat and current, biocompatibility. Some

applications are in micro pumps, medical equipments. Maeda et al [14] performed experiments with

the revolving tool on (ECSM) electro-chemical spark machining. For the machining of glass and

ceramic (these are insulating material) ECSM machining has been employed. Electrolyte has been

used as working fluid and work piece is dipped into working fluid and revolving tool is pressed on

the work piece with some load. A work piece was revolve so that it can give fresh working fluid into

the space between the work piece and the tool electrode in the experiments and machining soda lime

glass rod using a film type rod made of tungsten in a solution of NaCl. By setting the rotating speed

to 0, 0.30, 3.00 and 30.00 per min, new applied voltage was set to between 0 to 40 V and discharge

was observe at applied voltage 30V. As the result of increase of applied voltage the surface

roughness, depth and width of machines grooves were increased. The width of machined groove was

found to be small due to decrease in thickness of vaporization near the tool electrode as the rotation

speed increases. Kozak et al [16] investigated the nontraditional process because the use of un

conventional machining is increasing because it can machine glass, ceramic, composites which are

non conductive to heat and current. They stated some experimental facts about abrasive

electrochemical machining (ECM) and abrasive electrical discharge machining (EDM) which are




some superior technique and better control techniques. Kulkarni et al [17] studied the discharge

mechanism analysis of ECDM. In this study, author measures the time varying current to find the

basic mechanisms of rise in temperature and material removal rate and author has done experiment

at applied voltage 155 V and 3% HCL as the electrolyte in different three phases or different work

pieces such as Cu, tantalum, Si and brass. A gas bubble is formed which made of hydrogen, for a

short duration in a spark channel (highly conducting). Skrabalak et al. [18] studied a model based

on the rules of fuzzy logic control for study of the ECDM process. The experiment carried out in

solution of 6% NaNO2 with H2O and the most important parameters are current and electrode feed

at the fixed electrode temperature. The quality of surface and material removal rate both were

enhanced using adaptive fuzzy-logic control system which reduced surface roughness and no. of

micro cracks. Mediliyegedara et al. [19] investigated a study of an intelligent classification system

based on ANN for ECDM. Due to overheating of work material distortion in surface of work piece

takes place and reduction in MRR is taking place due to increase in electrode gap. In this process, Cu

tool with mild steel work piece and sodium nitride is used and the wave form shows the EDCP, AP,

SP, ECP and SCP by measuring the current and voltage. The pulse duration and duty ratio were

found to be 100ms and 50%. The average classification accuracy of the neural network with

SATLILS activation function was greater than the neural network with SATIL activation function.

Raghuram et al. [20] studied the effect of circuit parameters on the ECD process and studies the

effect of current and voltage at different electrolyte KOH and NaOH. In this process, the best circuit

configuration was proposed for machining of non conducting materials and the studies shows the

external circuit parameters had the effect on the discharge characteristics. The author had shown

voltage current behavior in ECD.

3. Objectives

Travelling (voyaging) Wire-ECDM is also known as TW-ECSM process. It is a combination of

ECM and EDM. Here a travelling brass wire is used as a tool. Objective was to using O-FAT (one

factor at a time) optimization technique to get effective combination of applied voltage ,electrolyte

concentration, feed rate, electrode distance. After the experiment, calculating the MRR and after that

using the surface texture machine to measure the surface finish.

i. To study the essential attributes of TW-ECDM transform and to recognize the significant

procedure parameters of TW-ECDM.




ii. To complete the essential investigations for deciding the scopes of critical procedure

parameters of TW-ECDM.

iii. To add to the scientific models connecting real process parameters, for example, electrolyte

concentration, feed rate of wire, pulse on time and voltage with MRR after that getting

surface roughness.

iv. To examine the impacts of the real process parameters on MRR and surface roughness.

4. Process Mechanism of TW-ECDM

Combination of ECM and ESM is used in TW-ECDM. Spark generation, bubbles formation, MRR,

deterioration of tool wire are the various phenomena used in TW-ECDM.

4.1 Formation of Gas Bubbles

There are mainly 2 types of chemical reactions that take place during the electrochemistry of

ECM process. These 2 reactions are:

Electrochemical reaction on the tool electrodes. As a result of the reaction there takes place

evolution of gas, oxidation and dissolution of electrode material takes place.

Chemical reaction in the electrolytic solution.

On the electrolyte boundaries these reaction takes place. In the electrolytic solution the movement of

ions takes place by:

Diffusion mechanism

Electric field migration in the solution

Flow causing the convection

As the voltage supply reaches the appropriate value chemical reaction starts on anode and cathode

terminal. These reactions take place at the gap between the electrodes in machining zone.

a. Cathodic reaction

Common reactions at the cathode terminal are plating due to metal ions and generation of

hydrogen gas bubbles.

M+ + e

- = M

Here M is material at anode

Hydrogen evolution takes place by following reaction




2H+ + 2e

- = H2 (in acidic electrolytic solution)

2H2O + 2e- = 2(OH

-) + H2 (in alkaline solution)

b. Anodic reaction

In a similar way to cathodic reaction there are 2 types of reaction at the anode. In the

electrolytic solution dissolution of ions takes place. Also at the electrode surface evolution of

the oxygen takes place.

M = M+ + e

-

2H2 +2 O = O2 + 4H+ + 4e

-

4(OH-) =2H2O +O2 +4 e

-

The formation of gas bubbles and the phenomenon of sparking take place in TW-

ECDM.

4.2 Principle of Spark Generation

In TW-ECDM the inter-electrode gap is very large as compared to ECM process. Due to the small

amount of current passing through the large inter electrode gap the MRR is small. A high voltage

D.C. power supply was applied between and the anode (auxiliary electrode) and the cathode (tool /

wire). In electrolyte solution the tool is immersed to depth of 2±3 mm. near the tool/wire the amount

of hydrogen bubble is generated is high. Electrolyte is evaporated and the formation of steam takes

place due to the heating of electrolyte. The gas bubbles are positively charged bubbles. Increasing

the supply voltage a threshold voltage can be attained and the formation of spark takes place in

between the gap and bubbles are also formed. Sparking doesn’t takes place between the electrodes,

but a layer of steam hydrogen is formed between the electrolyte and tool. The sparking voltage

depends on the conductivity of electrolyte concentration and tool geometry. If the diameter of wire is

small then the starting spark voltage is low. If the voltage is increased up to a particular limit then the

violent sparking may take place. Material is removed from work piece due to the localized sparking

because of the ionization process that occurs at high temperature which leads to melting and

vaporization. Fig 2.2 represents the sparking phenomena of TW-ECDM.




Fig. 4.1: Sparking Phenomena of TWECDM

4.3 Material Removal Mechanism

In TW-ECSM process, material is removed with the combined effect of electrochemical reaction and

electric spark action. Electrical spark generated is proportional to pulse energy of the spark because

of this material is removed which transform into heat during machining. The surface of the tool wire

and working component are not perfectly fine. There are irregularities in surface. These irregularities

are of micro level. So whatever is the closeness of tool wire with the work piece there is still some

gap left. Due to presence of micro gap between the tool and work piece electrolyte occupies the

space between them. This electrolyte results in the formation of bubbles and generation of heat. Thin

gas layer forms between the tool and work piece due ion formation. As the voltage increases a level,

breakdown of the bubbles start. This leads to formation of a conducting path due to ionization of the

bubbles. In this path current starts flowing. With each spark produced electron starts moving with

very high velocity from the cathode toward the work piece. These electrons when reaches anode

produces a shock impact on the surface. All this happens within a microsecond time. As electrons

hits with an impact, large heat generates. It leads to very high temperature. As this temperature

exceeds the melting point, material melts and finally evaporates. This impact is like a blast, that

creates crater on the work piece surfaces.




5. Experimental Setup

The setup for TW-ECDM was fabricated by a research scholar Mr. Navrattan. A proper approach toward the

process TW-ECDM was developed and working of setup was studied in detail for performing experiments.

TW-ECDM system consists of some subsystems as following:

a) Mechanical component; b) Electrolyte supply unit c) Electric Power supply unit

The setup of TW-ECDM process is shown in schematic diagram fig.5.1.

The direct DC voltage is applied between auxiliary electrode (+) and wire (tool electrode) (-). The wire just

touches the work piece and these are immersed into the electrolyte solution up to a certain depth. Stepper

motors are used to provide motion to the wire spool and job holder. Motor control unit (MCU) is used for

varying the speed of stepper motor and wire velocity.

Fig 5.1: schematic diagram of TW-ECDM setup

Fig 5.2: Photograph of TW-ECDM setup

5.1 Mechanical Components

Travelling wire ECDM setup has different mechanical sub system modules. The snapshot of Travelling Wire-

ECDM experimental set-up has been shown in fig. 5.2.




5.1.1 Machining Chamber

Perspex was used for fabrication of chamber for machining process. The rectangular box type machining

chamber has dimensions 650 mm x 405 mm x 500 mm. The thickness of Perspex plate is 12 mm. There is a

bottom plate and four other vertically oriented plates. Among three of plates with 8.5 mm thickness and the

cross vertical plates have dimensions 650 mm x 300 mm and thickness 8.5 mm. Longitudinal vertical plates

have dimensions 405 mm x 300 mm and thickness 8 mm and 12.5 mm. The wire feeding arrangement, job

holding arrangement and motion controlling unit are attached to the main machining chamber.

5.1.2 Wire Feeding and Controlling Unit

The non-conductive work piece can be fixed using the holding unit and submerging it in the electrolyte.

Connecting a stepper motor so as to receive end wire spool generally called as power spool so that we can feed

the wire at the zone where machining is done. The donator wire spool which is unconstrained also known as

dead spool. Keeping the wire almost straight along horizontal direction. Using the stepper motor, we can

change the feeding speed of the wire manually. Since the wire tension is one of the most critical parameter so

we use pulley based system to make it uniform throughout the process. Now this wire is passed between the

two plates and during passing between the gap it touches the plate. The plates are connected with the positive

pole of DC power supply and the wire or tool electrode is made cathode. The main requirement of the

experiment is that the wire should attain a particular speed during the experiment because wire breakage can

also occur so the speed of wire is to be controlled by stepper motor. In this unit the proper positioning of the

wire with respect to work piece before each experiment, for getting better results, has to be adjusted. In this

sub-system the movement of power spool unit (receiver end), dead spool unit (donator end), guide pulleys, are

to be controlled.

5.1.3 Job Holding Apparatus

For translating up and down, job holding apparatus has been mounted on a spindle type structure. A stepper

motor is applied for giving the motion to the job holding unit and a gear train for converting the rotating motion

to translating motion. For holding the job a hub is made and it is made of Teflon because Teflon has a property

to withstand a higher temperature. The whole job holding device has fastened with a vertical Perspex plate

which helps in keeping the job holder rigidly in horizontal plane.




5.2 Power Supply System

Using a continuous DC power supply in TW-ECDM. Input and output voltage is used as main DC power

supply unit (120 volt, 20 A). To control the frequency pulse generator is used. The D.C. output power

characteristics are observed by a Cathode Ray Oscilloscope is connected to observe the DC output power

characteristics. Some control units are used such as frequency control unit, voltage controlling unit. Current is

supplied to the wire which results in the generation of hydrogen gas bubbles which finally causes the electrical

discharge.

Fig.5.3 photograph of pulsed DC power supply system.

5.3 Electrolyte Supply System

The electrolyte supply unit is a reservoir of electrolyte. The temperature is very high during the machining

process which causes the evaporation and heating of electrolyte. So for maintaining the same level of the

electrolyte it is necessary to provide electrolyte to the pool. A flask is used as the electrolyte reservoir which is

kept at a higher altitude as compared to the level of electrolyte pool and a pipe is used to provide electrolyte to

the pool during the machining process drop by drop. Generally KOH or NaOH solution is used as the

electrolyte solution. The electrolyte is added to the pool from the reservoir drop by drop rather than flow from

pipe. If electrolyte is fed with pipe it will reach the pool at very high velocity causing splash and waves into the

electrolyte pool and the formation of insulating layer of gas bubbles will be disturbed. As the evaporation rate is

slow in this process, the electrolyte should be added slowly. By mixing salt or water electrolyte concentration

can be increased or decreased.




6. Experimental Methodology

Three process parameters are considered for conducting experiments on TW-ECDM. The optimization

technique known as One-factor-at-a-time (OFCAT) was used for designing of the experiments. A brass wire

(0.25mm diameter) has been selected as the tool electrode. Electrolyte selection is also one of the important

parameter for this kind of machining processes because the chemical reaction depends upon the concentration

of electrolyte. NaOH solution is selected as the electrolyte for this experiment. The electrolytic concentration

varied from 9%, 13%, and 17% wt. The other important decision was to select the power supply nature and

the range of applied voltage. Here a continuous DC power supply was selected and experiments were done at

three different voltage levels: 25 V, 29 V and 32 V. The experiments were done according to OFAT (one-

factor-at-a-time) experimental design. During experimentation some of the process parameter were kept

fixed, are listed in Table 5.0.

Table 6.1: Fixed Process Parameters

FIXED PARAMETERS DESCRIPTION

Work piece material Glass

Electrolyte NaOH

Effective wire length 25 mm

Wire tension Constant

Tool material Brass wire(.25 mm diameter)

Wire and work-piece Touching each other

The influence of the above process parameters on MRR on the basis of previous research and experiments

and the appropriate range of the process parameters for TW-ECDM have been mentioned.

a) Applied Voltage The material removal rate is low when the applied voltage is low and it increases with the increase in applied

voltage but at very high voltage there is a possibility of rapture of the sample. The range of applied voltage used

in the experimentation is 15-35 volt.

b) Electrolytic Concentration

Electrolytic concentration is between the range 10% to 30%.The electrochemical reactions takes place between

counter electrode at higher electrolyte concentration (30%) and tool electrode (wire) and gas bubbles formation

at the sparking zone increases which results the generation of a higher number of sparks.

c) Velocity of Travelling Wire




Wire velocity is a factor that influences the performance of TW-ECDM process. When the wire feeding rate is

higher, the discharge cannot be uniform and the wastage of wire is more. Higher wire feeding rate results in

higher operating cost. Too low wire velocity has also some results as frequent breakage of wire can take place

and it will reduce the productivity. So there is always need an optimum wire speed with which the TW-ECDM

operation is done efficiently.

d) Wire Tension

The wire tension setting should be at maximum stretched condition of loading so that the wire is perfectly

horizontal at the machining zone to avoid wire rupture. For this condition the wire is passed through upper and

lower wire guide and by tensioning rollers. It is also constant.

e) Wire feeding rate

Feed rate is set firstly before machining. It can be handle manually or automatically. Its appropriate range is 60

-120 mm/sec. Very low feed rate will result in breakdown of the wire. So its proper maintenance is very

important. Very high feed rate results low discharge and MRR will be very less.

f) Type of electrolyte

Electrolyte selection is also one of the main factors. For particular machining alkaline salt solution has to be

used. For TW-ECDM process generally NaOH and KOH solution are used. NaOH solution is selected for

experiments.

7.1 Experimental Modeling

On TW-ECDM set up, Number of experiments was conducted and the experiment was done in two sets.

For conducting experiments on TW-ECDM three process parameters have been considered. OFAT (One-factor-

at-a-time) methodology was used to conduct the experiments. In the first step, By keeping two parameters

fixed, applied voltage was changed and fixed parameters are electrode distance and electrolyte concentration.

On the accomplishment of experiments the value of applied voltage which were having maximum material

removal rate was known. Now in the second step, Electrolyte concentration is varied by keeping two

parameters fixed which are applied voltage and inter electrode distance and maximum material removal rate is

known. After this step the value of electrolyte concentration having maximum MRR is known. In step three the

inter electrode gap is varied by keeping two others parameters constant. Maximum MRR is known and by

cutting the slides from between surface finish is measured on the surface texture machine. The experiments have been done in two sets.




7.2 Influence of Parameters on Surface Finish

As per the process result it is evident that surface finish is the function of applied voltage, electrode distance,

electrolyte concentration and MRR. As the applied voltage is increasing, MRR is also increasing and surface

finish is decreasing and as the electrolyte concentration is increasing result of that sparking is increasing and

MRR is also increasing and surface finish is decreasing. At very large electrode distance surface finish is

decreasing and at very low electrode distance surface finish is also decreasing and same case is with the MRR.

So to get best optimization optimum parameter was chosen given in previous table. To get the surface finish,

the inter electrode distance should be neither too small nor too large.

8. Conclusion and Future Scope

Travelling Wire-ECSM can be used for machining the insulating material on large scale. OFAT (one-factor-at-

a-time) technique is used to perform experiments on TW-ECSM setup. Effective combination of maximum

MRR and better surface finish is subject of concern. If MRR is high than surface finish will be low so by

optimization of parameters we can get optimum MRR and good surface finish. Several inferences has been

drawn from the work done:

1. As the voltage is increasing, MRR is also increasing and surface finish is decreasing. The reason behind

that is with increase in applied voltage, the HAZ is increasing because of increment in spark generation.

2. As the electrolyte concentration is increased, from the experiments, we saw MRR is also increasing and

surface finish is decreasing.

3. From the experiments, I observed at very low electrode distance i.e4cm, the surface roughness value is

above 40µm and at very high electrode distance i.e16cm, the surface roughness is 38.723µm so it can

stated electrode distance should be optimum to get surface finish higher. Optimum value of parameters

to get higher surface finish are 26V applied voltage, 9cm inter-electrode gap and 10% electrolyte. The

best surface finish was got which is 5.53µm.

Future scope of TW-ECSM is given as follows:

1- Efficiency of the setup should be increased as I observed from results surface finish is best at low MRR.

Work can be done in the field of parameter optimization.

2- In case of very complex shapes, accuracy is major concern because accuracy is not good in this method

due to sparking and heat affected zone (HAZ).




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